Recently, the approaches focusing individual susceptibility to drug have been taken toward drug discovery/development. The backgrounds of patients are diverse, and in fact, there are some cases in which idiosyncratic toxicity is suspected as the reason of drug development failure. Given the acceleration of aging in Japan and the diversity of patients' drugs, we could need to update drug safety strategy. Nevertheless, the conventional drug safety assessment is conducted using models such as homogenous cell lines and normal animals, and it is not enough to understand or predict the individual susceptibility to drugs in patients. As an approach for predicting individual susceptibility to drug in patients, (1) deeply understand the background of the patients, (2) create a hypothesis based on that background, and (3) extrapolate the hypothesis experimentally are applied. To promote these stepwise approaches, first, it is necessary to understand the type of disease, medical history or co-/multi-morbidity, and trend of polypharmacy in patients. Then, it is considering susceptibility to drugs in a specific patient, so that preparing an appropriate in vitro model. In particular, regarding in vitro model, recent advanced models such as iPS cell-based platforms have been versatile for some assays and are highly expected to be leveraged for predicting individual susceptibility to drugs in patients. In the presentation, I would like to discuss a concept to assess individual susceptibility to drug, including examples, and expand the future potential.